A leading opposition figure in Georgia has formally launched a new political party to challenge the rule of President Mikheil Saakashvili.

Former parliament speaker Nino Burjanadze, a one-time ally of the president, launched her Democratic Movement-United Georgia party Sunday in Tbilisi, at a founding congress attended by more than 2,000 supporters.

In an address, Burjanadze called for early elections to bring "new authorities to power." She also accused Mr. Saakashvili of mishandling Georgia's military conflict with Russia in August, and said, in her words, that authorities in "any civilized nation who led their country to disaster" would resign.

Critics have accused Mr. Saakashvili of triggering the Russian invasion when he ordered Georgian military forces to regain control of the pro-Russian breakaway territory of South Ossetia. Western military analysts and Saakashvili opponents say Georgia stood no chance of prevailing in the conflict.

Burjanadze earlier served as the country's interim president. She resigned earlier this year as speaker of parliament, and later sharply criticized Mr. Saakashvili for his role in the Georgian-Russian conflict.

The Burjanadze announcement came on the fifth anniversary of Georgia's Rose Revolution -- the peaceful 2003 uprising against former Georgian President Eduard Shevardnadze that brought Mr. Saakashvili to power.